Existing fuel cells generally are a stacked assembly of individual fuel cells, with each stack producing high current at low voltage. The typical reactor construction involves reactant distribution and current collection devices brought into contact with a layered electrochemical assembly consisting of a gas diffusion layer, a first catalyst layer. With the exception of high temperature fuel cells, such as molten carbonate cells, most proton exchange membrane, direct methanol, solid oxide or alkaline fuel cells have a layered planar structure where the layers are first formed as distinct components and then assembled into a functional fuel cell stack by placing the layers in contact with each other.
One major problem with the layered planar structure fuel cell has been that the layers must be held in intimate electrical contact with each other, which if intimate contact does not occur the internal resistance of the stack increases, which decreases the overall efficiency of the fuel cell.
A second problem with the layered planar structured fuel cell has been that with larger surface areas, problems occur to maintain consistent contact with both cooling and water removal in the inner recesses of the layered planar structured fuel cell. Also if the overall area of the cell becomes too large then there are difficulties creating the contacting forces needed to maintain the correct fluid flow distribution of reactant gases over the electrolyte surface.
Since both reactants are required to flow within the plane of the layered planar chemical reactor, at least four and up to six distinct layers have been required to form a workable cell. These layers are usually manufactured into two separate chemical reactors components. A chemical reactor stack is, then, formed by bringing layers into contact with each other. In forming the chemical reactor stack by contacting the layers, gas diffusion must be allowed within the layers to prevent gas from leaking from the assembled chemical reactor stack. The assembled stack usually has to be clamped together with significant force in order to activate perimeter seals and reduce internal contact resistance. Compressing layers together using brute force is inefficient and expensive.
Electrical energy created in the fuel cell has to travel between layers of material compressed together before it can be used. These layers include membrane electrode assemblies, gas diffusion layers, separator plates etc. The resistance to the transfer of electrical energy through each layer and between layers also affects the performance of the fuel cell. The contact pressure and contact area that can be achieved between the layers of the fuel cell stack is directly proportional to the conductivity of these components and hence the performance of the fuel cell stacks.
Laying out layers of material and compressing them together using the brute force approach of traditional fuel cell stacks is inefficient and expensive. In addition, such designs suffer from long term performance degradation because of thermal and mechanical cycles that occur during the operation of the fuel cells.
In manufacturing fuel cell stack assemblies using this typical layering approach of all the components, accurately aligning the layers is difficult. Inaccurate alignment has a detrimental effect on the performance and durability of the fuel cell stacks.
A need has existed for micro, or small fuel cells having high volumetric power density. A need has existed for micro fuel cells capable of low cost manufacturing because of having fewer parts than the layered planar structure fuel cell. A need has existed for micro fuel cells having the ability to utilize a wide variety of electrolytes. A need has existed for a micro fuel cell, which has substantially reduced contact resistance within the fuel cell. A need has existed for a micro fuel cell, which has the ability to scale to high power density fuel cells. A need has existed for a micro fuel cell having an increased reactant surface area. A need has existed for a fuel cell capable of being scaled to micro-dimensions. A need has existed for fuel cells capable of being connected together without the need for external components for connecting the fuel cells together.
A need has existed for a compact fuel cell with high aspect ratio cavities. The aspect ratio of the fuel cell is defined as the ratio of the fuel cell cavity height to the width. Increasing this ratio is beneficial for increasing the efficiency of the fuel cell.
A need has existed to develop fuel cells topologies or fuel cell architectures that allow increased active areas to be included in the same volume, i.e. higher density of active areas. The present embodiments meet these needs.